Desulfurization process



United States Patent 3,413,307 DESULFURHZATION PROCESS Barry N.Heimlich, Union, and Thomas J. Wallace,

Elizabeth, N.J., assignors to Esso Research and Engineering Company, acorporation of Delaware No Drawing. Continuation-impart of applicationSer. No. 434,643, Feb. 23, 1965. This application May 10, 1965, Ser. No.454,693

2 Claims. (Cl. 260329.3)

ABSTRACT OF THE DISCLOSURE Organic sulfur is oxidized by means of amixture of an organic carboxylic acid, an oxy-mineral acid and anoxidizing agent. The oxidation serves to convert the sulfur to a formfrom which desulfurization may take place more readily. This serves toreduce pollution problems.

This case is a continuation-in-part of our earlier filed application,U.S. Ser. No. 434,643, filed Feb. 23, 1965, and entitled ADesulfurization Process.

This invention relates to an improvement in the desulfurization of ahydrocarbon mixture. More particularly, the invention concerns thedesulfurization of heavy hydrocarbon fractions, including residua. Moreparticularly, this invention pertains to a method for convertingbivalent sulfur selectively to the sulfone state, to facilitate thermalor caustic desulfurization. This is accomplished by utilizing a uniquemixed acid catalyst which with great selectivity successfully convertsthe bivalent sulfur to sulfones. The mixed acid catalyst compriseshydrogen peroxide, acetic acid and sulfuric acid in critical amounts.

Air pollution is becoming an increasingly important problem to theentire world. Residual fuel oils that contain significant quantities ofsulfur form noxious S0 upon combustion and recent studies,substantiating this, indicate that the amount of noxious S0 in theatmosphere is continually growing. These compounds, aside from lendingto a generally high level of discomfort for those who are forced to livein areas where they are present, also constitute an extremely dangeroushealth hazard and have contributed greatly to the growing presence ofrespiratory diseases.

Recently, a U.S. Patent 3,163,593 was issued concerning a method ofdesulfurizing heavy oils. This patent teaches a method for changing thestate of sulfur which is found in heavy hydrocarbon oils by oxidationwith an acid catalyst. The feed stock utilized in that invention is aheavy hydrocarbon oil, that is to say a hydrocarbon oil of which atleast 50% by volume boils above 250 C. To oxidize the sulfur in theseheavy oils, organic peracids, e.g., performic or peracetic acid ormixtures of hydrogen peroxide with formic or acetic acids are utilized.This is somewhat satisfactory, however, it does present substantialdrawbacks. Because of the appreciable solubility of these acids in oils,the use of concentrated organic acids causes significant acid recoveryproblems. Accordingly, it would be preferable to use dilute aqueous acidmixtures in order to reduce the loss of acid by dissolution in the oil.In the instant invention, it has unexpectedly been found that a uniquedilute aqueous acid catalyst media affords excellent rate of oxidationwithout significant difiiculties in acid recovery. This is accomplishedby using dilute aqueous solutions of mixed acetic and sulfuric acids ordilute halogenated acetic acids in mixture with aqueous hydrogenperoxide or other oxidants.

According to one aspect of this invention, a process has been discoveredin which residua is treated with a dilute aqueous solution of H 0 aceticacid and H 80 to convert the bivalent sulfur, which is present inorganic com- "ice pounds, selectively to the sulfone state whereby thedesulfurization of the sulfone may be facilitated by thermal or causticmeans. More specifically, the treatment of the present inventionconcerns a method by which a residua, which is a heavy petroleumfraction whose initial boiling point is usually about 600 F. is treatedwith a specific oxidizing agent, which comprises an aqueous solution ofH 0 acetic acid and H 30 Contacting this mixed acid catalyst with theorganic sulfur compounds found in a residua results in the oxidation ofthese organic compounds to the sulfone state. The sulfone may then becleaved by means of caustic or heat to produce a product which issubstantially sulfur free.

This invention will be most effective when utilized to treat heavysulfur bearing residua. Residua is what remains after naphtha and gasoil have been removed from a crude oil by atmospheric distillation. Ithas an initial boiling point of about 600-650" F. This would includeresidua from the following crudes which are particularly high in sulfurcontent: Safaniya, Kuwait, Bachequero, Arabian, to name a few. Thesecrudes will profit greatly by the treatment of the instant invention.The previously known treatment of hydrodesulfurization is not nearly soeffective as this process since it often results in too much expense oris unsuited for use with the particular sulfur compounds which onedesires to convert. The expense is associated with the fact 6 to 10moles of hydrogen must be consumed per mole of sulfur. This is due tothe high aromatics content of the residua.

The instant invention applies to the treatment of all hydrocarbon oilsin which a substantial number of molecules contain a sulfur atom as Wellas carbon. In particular, this invention is extremely helpful intreating any hydrocarbon fraction which contains thiophenes or thiophenederivatives. This invention may therefore be utilized with organicsulfur-containing whole crude oils or reduced crudes which boil above300 F., preferably above 600 F. Thus, the invention has an extremelywide range of applicability. However, it is believed it will find itsmajor use in treating residua, either atmospheric, vacuum, or fromassorted processes such as catalytic cracking. Other than resins,lubricating oils, transformer oils, gas oils and kerosenes may betreated. In fact, any petroleum fraction boiling between 300 F. and 1050F., preferably between 600 F. and 1050 P. which contains organic sulfursmay be improved by the process of this invention. Most preferably, theinvention will be utilized to treat residua as described above.

With respect to the organic sulfur compounds which may be utilized inthe instant invention, these are numerous and varied in scope. Someexamples of the organic sulfur compoundn to be treated aredibenzothiophene, benzothiophene, naphthothiophene,naphthobenzothiophene, diphenyl sulfide, alkyl sulfides and derivativesthereof. In general, we are concerned with thiophene derivatives andalkyl, aryl and aralkyl sulfides. Exemplary of the most dilficult todesulfurize of these compounds is dibenzothiophene, which is also themost prevalent class of sulfur compounds in residua. Since it is anexcellent example of the general class of organic sulfur compounds foundin residua, it will be used as an example to illustrate the entireclass. There is no intention, however, to be bound by any particularmechanism or illustration of an entire class.

The organic sulfur compound, as illustrated by dibenzothiophene, iscontacted with the mixed acid catalyst of the instant invention. Thismixed acid catalyst consists of an aqueous solution of sulfuric acid,acetic acid and hydrogen peroxide. The following ratios of the mixedacid catalysts are applicable; generally about 1 to 50% of volumeconcentrated sulfuric acid is combined with about 1 to 50% of glacialacetic acid by volume and about 2 to 10 moles of hydrogen peroxide permole of sulfur compound. Preferably about 10 to 40% by volume ofsulfuric acid, 5 to 25 parts by volume of acetic acid and 2 to 10 moleof hydrogen peroxide per mole of sulfur compound are used. In its mostpreferred form, this invention would involve the use of 25 to 35% ofsulfuric acid by volume, 10 to 20% of acetic acid by volume and 2 to 10'moles of hydrogen peroxide per mole of sulfur compound.

A variety of reagents may be substituted for the hydrogen peroxide; theyinclude alkali metal periodates, perchlorates, chromates andpermanganates, metal oxides such as manganese dioxide or chromic oxide,perchloric and hypochlorous acids, hydroperoxides such as tertiarybutylhydroperoxide, peracids such as performic, peracetic,pertrichloroacetic, perbenzoic and perphthalic acids. The acid systemmust be a mixed acid system; in place of sulfuric acid other oxy-mineralacids such as nitric, boric, phosphoric, chloric and perchloric acids,may be utilized. The acetic acid can be substituted with formic,chloroacetic, dichloroacetic, trichloroacetic, trifiuoroacetic, benzoic,phthalic, or terphthalic acids. The organic acid can be branched, i.e.trimethylacetic and it can contain other funtcional roups such as NH NHO and HS to 4 EXAMPLE I The following example indicates the relativesuccess in converting dibenzothiophene which is attained with vari ousoxidizing mixtures. In all instances, the dibenzothiophene was treatedunder identical conditions. About 5.14 gm. of dibenzothiophene in asolution made up with 100 cc. of highly refined white oil, to which 5cc. of n-hexadecane was added to serve as a chromatographic standard,was contacted with various oxidizing mixtures for a period of 120-minutes in a glass vessel. The temperature utilized for all runs was 212F. and ambient pressures were also utilized. The white oil solutions ofthe dibenzothiophene and the oxidizing mixtures were separately heatedto reaction temperature and then brought into reaction in a wellagitated flask. Aliquot samples of the oil were taken initially andperiodically as the runs progressed and were analyzed by gaschromatography. The conversion of diben- Zothiophene was determined bymeasuring its peak area on the chromatograph relative to the peak areaof the nhexadecane. The reaction products were isolated and found to bedibenzothiophene sulfone by gas chromatography, infra-red and by meltingpoint. The following table, Table 1, indicates the improvement of theinstant name a few. 29 invention.

Run 00. 30% Cc. glacial Cc. water Ce. cone. K min- Percent DBT 0. H203acetic acid H25 04 conversion 16. 6 10 90 0032 30 (120 min.) 16. 6 10 8010 0189 68 80 min.) 16. 6 50 50 0255 80 60 min.) 16. 6 50 50 0202 82(100 min.) 16. 6 50 49 1 296 98 min.) 16. 6 50 40 10 547 94 (5 min.) 16.6 75 25 6941 90 (24 min.) 16. 6 100 346 90 7 min.) 16. 6 65 25 0866 90(27 min.) 16. 6 65 10 100 90 (23 min.) 16. 6 75 25 Nil No conversion.16. 6 50 50 0156 85 (120 min.)

The oxidizing medium of this invention comprises broadly an organiccarboxylic acid, an oxy-mineral acid and an oxidizing agent.

The preferred oxdation medium is made up by adding 5 to 25 parts byvolume of glacial acetic acid and to 40 parts of concentrated sulfuricacid by volume to 55 to 75 parts water to which 10 to parts .of 30%hydrogen peroxide has been added. From 0.5 to 5 volumes of the organicsulfur containing oil can be treated with 1 volume of the oxidationmedium, For purposes of illustration, this invention will be discussedin terms of dibenzothiophene, however, it should be noted that anyorganic sulfur compound, as defined previously, may be treated in thesame fashion.

The thiophene, or thiophene derivative, containing oil should becontacted with the oxidation medium for a period of 10 to 120 minutes,preferably 20 to 90 minutes, most preferably 30 to 60 minutes.Temperatures for the reaction may vary from 100 to 300 F., mostpreferably from 200 to 250 F. Pressures may vary from atmospheric tosuperatmospheric. At temperatures below 225 F., ambient pressures may beutilized. At temperatures of about 225 to 300 F. slightlysuperatmospheric pressures such as 5 to 50 p.s.i.g. may be utilized. Thereaction time for the conversion of thiophene to the sulfone is usuallyabout to 60 minutes, during this time the reaction is about 90 to 100%complete.

After the thiophene, or other organic sulfur compounds, have beenconverted to the sulfone, the ring of the sulfone may be opened by avariety of methods. The sulfone may be contacted with an alkali metalhydroxide as described in our copending application U.S. Ser. No.434,643, or alternately the sulfone ring may be opened as suggested inU.S. Patent 3,163,593 by means of extreme heat. There is no intention tolimit this application to either of those procedures and any method inwhich the sulfur is removed from the Sulfone is also applicable.

These data clearly show that the addition of sulfuric acid to theaqueous acetic acid-hydrogen peroxide oxidation medium greatly increasesthe rate of oxidation of dibenzothiophene despite the fact that sulfuricacid alone is a very poor oxidation catalyst, as shown in runs 11 and12. The addition of 10 cc. of H to the mixture containing 10 cc. ofacetic acid in run 2 brought about an increase in the oxidation ratecomparable to increasing the amount of acetic acid to 50 cc. in run 4.The addition of 1 cc. of sulfuric acid in run 5 and 10 cc. of sulfuricacid in run 6 brought about very marked improvement. The addition of the1 cc. of sulfuric acid, with 50 cc. of glacial acetic acid, resulted ina 98% conversion in 15 minutes. This rate is almost as good as thatwhich was effected in run 8 with 100 cc. of glacial acetic acid and no H50 Furthermore, the presence of only 10 cc. of sulfuric acid in run 6brought about a result which was markedly superior to the use of 100 cc.of glacial acetic acid alone. Of more practical importance, the presenceof 25 cc. of sulfuric acid and 10 cc. of acetic acid in run 9 broughtabout a rate that is comparable to that with 75 cc. of acetic acid andno H 80 in run 7. Also, 10 cc. of sulfuric acid and 25 cc. of aceticacid in run 10 was superior to the use of 75 cc. of acetic acid alone.Thus, it is possible to use relatively dilute acid media and stillaccomplish high rates of oxidation.

From the above it is apparent that this invention represents asignificant improvement in the oxidation art. The addition of smallquantities of sulfuric acid will greatly reduce the amount of aceticacid needed to maintain a high reaction rate and therefore permit theuse of large amounts of water. Because acetic acid is more soluble inwater than in oils, good recovery of the acetic acid will be possible.Furthermore, the use of dilute aqueous media reduces the possibility ofemulsion formation, which would complicate acid recovery in a commercialprocess.

Since small amounts of sulfuric acid will greatly increase the oxidationrate, large volumes of water may be tolerated in the reaction mixture.The use of more dilute media will result in a considerable financialsaving in process equipment and heat requirements. Most important ofall, there is considerably less hazard in handling H when it is diluterather than when it is concentrated. The sulfuric acid which is used inthis reaction will also be dilute due to the large amounts of waterwhich are present. It is well-known in the art that dilute sulfuric acidcan be more readily recovered from a process than can be concentratedacid. Naturally, a great saving in the amount of glacial acetic acidneeded will also ensue since sulfuric acid may be utilized as aneffective substitute for large amounts of the acetic acid. Since adilute acid medium is employed, separation of the hydrocarbon from theaqueous phase is also easier, since emulsions tend to form in thepresence of concentrated acid solutions.

It is also within the scope to utilize halogenated acetic acids such asmono-, di-, and tri-chloroacetic acids, as catalysts along the H 0 Inthis instance, sulfuric acid will not be needed to speed up the reactionsince it proceeds satisfactorily. This is further substantiation of theadvantage of having strong acids in mixture with acetic acid in theoxidation medium, since the haloacetic acids have very much higher acidstrengths than acetic acid itself. Furthermore, because the haloaceticacids are stronger acids and have higher polarities, they are much lessoil soluble than acetic acid and would be more readily recovered. Theadvantages of using haloacetic acids are illustrated in the examplebelow.

EXAMPLE II These experiments were conducted in the same manner as thosediscussed in the previous example except that the indicated haloaceticacid was used in place of the sulfuric-acetic acid mixtures. Again 5.14gm. of dibenzothiophene and 5 cc. of n-hexadecane (chromatographicstandard) were dissolved in 100 c. of white oil and heated to 212 F.This oil was then brought into reaction with oxidation mixtures made upof 0.435 mole of acid catalyst indicated below in 75 cc. of water towhich 16.6 cc. of 30 weight percent H 0 was added. Again aliquot samplesof the oil were withdrawn and analyzed by gas chromatography todetermine the extent of dibenzothiophene disappearance. The reactionproduct was found to be dibenzothiophene sulfone.

These runs clearly show the advantage of using haloacetic acids in placeof acetic acid. The haloacetic acids are 16 to 57 times as effective asan equimolar quantity of acetic acid. Also, the oxidation rates withthese very dilute aqueous solutions are comparable to the use of 75volume percent acetic acid. The acetic acid used in run 1 was 25 volumepercent for comparison.

Although this invention has been described with some degree ofparticularly, it is intended only to be limited by the attached claims.

What is claimed is:

1. A process for oxidizing bivalent sulfur which is found in a residua,which comprises contacting in an aqueous media the saidsulfur-containing residua with 2 to 10 mole of H 0 per mole of sulfurand 1 to 30 mole of haloacetic acid per liter of residua at reactionconditions whereby the said bivalent sulfur is oxidized.

2. Process of claim 1 wherein the said haloacetic acid istrichloroacetic acid.

References Cited UNITED STATES PATENTS 2,624,664 12/1953 Mowry et a1.71-2.5 3,005,852 10/1961 Freyermuth et al. 260607 3,006,963 10/1961 Bucet a1 260-607 3,102,148 8/1963 Campbell et al. 260-607 3,163,593 12/1964Webster et al 208-240 OTHER REFERENCES Kambara et al: Chemical Abstracts46: 1795 (1952).

Fieser et al.: Advanced Organic Chemistry (Reinhold Pub. Co., New York),1961, pages 360362.

Kalabina et al.: Chemical Abstracts 60: 16301631 1964).

HENRY R. JILES, Primary Examiner. C. M. SHURKO, Assistant Examiner.

